The package is to toward a cost oriented business of manufacturing. Generally, an integrated circuit die is enclosed in plastic packages to be resistant to hostile environments and to provide electrical connections between the semiconductor die and printed circuit boards. A package usually includes a metal leadframe, a semiconductor die, bonding material to attach the semiconductor die to the leadframe, bonding wires connecting pads on the semiconductor die to lead fingers of the leadframe, and a plastic encapsulant material sheltering all the components mentioned above but a portion of lead fingers for electrically connecting to external pads on printed circuit boards.
A portion of lead fingers of a leadframe is internal to the package with encapsulant surrounding the portion of lead fingers and the die pad of a leadframe, wherein the die pad of a leadframe is the central supporting structure of a leadframe. Another portion of lead fingers of a leadframe is external to the package without encapsulant material surrounding and electrically connected to pads on printed circuit boards. After the die is coupled to a leadframe with wirebonds, the die, die pad of leadframe, and a portion of lead fingers are encapsulated in plastic by flowing plastic over them at high temperature and pressure. Before mounting the package on the printed circuit boards, a mold is necessary for bending the extended lead fingers at specific angle with small tolerance of deviation in mass production. Generally, it is costly to design and construct a mold and it is hard to modify the specification of a mold.
While used in an optical system, a semiconductor die is usually required to receive light and manipulate the information from the light according to the properties of light. A clean mode package (CMP) is employed especially for designs in optical systems. The clean mode package provides a transparent encapsulant material covering a semiconductor die and a leadframe despite a portion of a lead connected to pads on printed circuit boards. A light source passing through the encapsulant material is further transferred into electrical signals by the semiconductor die, i.e. photo sensors.
A problem with conventional CMP is that only the top side of a die pad of a leadframe is utilized. In an optical system like pick-up head of a compact disk (CD) system or a digital video disc (DVD) system, the requirement about reducing the size of the system construction is in great demand, in particular, in mobile devices. A prior art in exploiting the area utilization of printed circuit boards to save space shown that a daughter printed circuit board is obligated in an optical system. Additional connections between mother printed circuit board and daughter printed circuit board are necessary. The connections can use a socket on the mother board for the daughter printed circuit board or solderable materials between the mother board and daughter board. The oxidation of the metal material of socket and the solderable materials causes deterioration of the reliability. Although the other side of the mother printed circuit board is employed, cost for a system with additional daughter printed circuit board increases and reliability for a system connecting a complex component decreases.